The present invention relates to a band member forming apparatus in which a tread is adhered on a breaker to form a band member.
In the production of a radial tire or other tire, in general, there has been employed a green tire production method in which a band member (or breaker band) is produced over a special drum in advance by adhering a tread on a breaker, and connected to a toroidal carcass which is formed over another drum.
A band member forming apparatus used in the above method are provided with a rotary drum as shown in FIG. 5 or 6. In the band member forming apparatus 60 shown in FIG. 5, a rotary drum 62 having a drum shaft 61 is made of a plurality of drum segments 63 each of which is in the form of an arc in a side view thereof. In addition, the band member forming apparatus 60 is provided with an air bag 64 in the form of a hollow which is an expansion and contraction means L for moving the drum segments 63 in radial directions. The air bag 64 is placed over the outer periphery of a supporter 66 attached to the drum shaft 61. When the drum is contracted, the air bag 64 is contracted so that the drum segments 63 are withdrawn inside as shown in an upper half portion of FIG. 5. When the air bag 64 is expanded, the drum segments 63 are pushed radially outward so that the outer diameter of the rotary drum 62 is expanded as shown in a lower half portion of FIG. 5. Then, a breaker and a tread are applied over the outer periphery of the rotary drum 62. The drum segment 63 is integrally provided with an engagement portion 67 of which cross section is hook-shaped so as to restrict the amount of the diameter expansion. The engagement portion 67 is engaged with a projection 69 of a restriction ring 68 to restrict the expansion diameter amount x.
A band member forming apparatus 70 shown in FIG. 6 is provided with air cylinders 71 as an expansion and contraction means in place of the air bag 64. The number of air cylinders 71 is the same as that of drum segments 72. In this case, the expanded length of the air cylinder 71 is considered as an expansion amount of the drum diameter. Furthermore, the band member forming apparatus 70 is provided with a restriction block 74 so as to keep a predetermined expansion length. An expansion length x defined by the restriction block 74 is considered as the expansion amount of the drum diameter.
In FIGS. 5 and 6, the breaker and tread are indicated at 75.
FIG. 7 is a diagram showing the positions of the drum segments 63 (72) when viewed in a direction of an arrow A of FIGS. 5 and 6. There is shown the positions of the drum segments 63 (72) at the time of contraction and expansion in upper and lower half portions of FIG. 7, respectively. As seen from FIG. 7, in the conventional apparatus, a peripheral surface is, at the time of contraction, formed with respective longitudinal end edges of the drum segments 63 (72) kept in contact with one another. On the other hand, at the time of expansion, a space a exists between the drum segments 63 (72) adjacent to each other.
According to the conventional apparatus, it is required to use the restriction ring 68 or restriction block 74 in order to keep the predetermined expansion diameter amount x. Moreover, it is necessary to provide variously sized restriction rings 68 or restriction blocks 74 for different kinds of tire. Furthermore, every time the diameter of a tire is changed, the restriction ring 68 or restriction block 74 should be replaced. Consequently, management of parts and preparatory working are complicated.
Furthermore, the air bag 64 or air cylinder 71 has a limited effective stroke. In the case where a tire having a greater size than the limited effective stroke is to be formed, it is required to use a rotary drum provided with expansion and contraction means having a greater effective stroke.
In the conventional apparatus, the spaces a exist between the drum segments at the time of expansion. Accordingly, a band-like material such as a breaker is likely to come into a polygonal form when applied over the rotary drum, which consequently causes an undesirable quality.